Generally in automotive assembly lines, for improved efficiency in assembling, a rotary tool such as a nut runner is used to fasten screws such as bolts and nuts. The nut runner rotated by a motor achieves fastening of screws at high speed and generates a reaction force corresponding to the fastening torque of the screw, which needs to be supported. In the case where a suspension unit is secured to a vehicular body, a large torque is necessary for fastening, resulting in a large reaction force that cannot be supported by hands of an operator.
Patent Document 1 discloses a screw fastener including a nut runner that is freely movable, to a required extent, using movement of a slider, rotation of a parallel link, and up-down movement of an elevation plate, so that an operator can hold and move the main body of the nut runner in horizontal and vertical directions as desired. The reaction force of fastening torque from the nut runner is transmitted to the slider via the parallel link to reduce burden to the operator.
[Patent Document 1] Japanese Patent Application Publication No. JP-A-2005-177910